1. Field of the Invention
The present invention relates to an anti-thief security sensor assembly of a type wherein while an infrared beam emitted from an infrared beam projecting unit is constantly received by an infrared beam receiving unit, an alarm is generated when an intruder traverses across the path of travel of the infrared beam from the infrared beam projecting unit towards the infrared beam receiving unit.
2. Description of the Prior Art
The anti-thief security sensor assembly is known in which a beam projector of an infrared beam projecting unit and a beam receiver of an infrared beam receiving unit are installed at opposite ends of a rectilinear guard area spaced an appropriate distance from each other with their optical axes aligned with each other. The infrared beam receiving unit is so operated that when the receiver senses the infrared beam the receiver can output an electric signal of a signal level proportional to the amount of the infrared beam received. The electric signal so outputted is, after having been amplified by an amplifier circuit, processed by a detecting circuit to remove a disturbance light component therefrom and then to convert it into a signal of a level proportional to the received beam signal, and the converted signal level from the detecting circuit is subsequently determined by a signal discriminating circuit as to whether or not the level of the converted signal is lower than a predetermined detection level. In the event that the level of the received beam signal attains a value lower than the predetermined detection level as a result of the infrared beam from the beam projecting unit towards the beam receiving unit having been intercepted by traverse of an intruder, the signal discriminating circuit outputs a detection signal with which an alarm generator is driven to output an alarm signal that may be utilized to warn that the intruder has entered the guard area.
The anti-thief security sensor assembly is generally capable of monitoring the guard area ranging from a rectilinearly close distance to a rectilinearly long distance of a few hundred meters, and the longer the rectilinear distance, the more difficult it is to install the beam projector and the beam receiver with their optical axes aligned with each other as accurately as possible at respective locations that are spaced a distance from each other. Accordingly, the conventional anti-thief security sensor assembly includes a sighting instrument so as to facilitate the alignment of the respective optical axes of the beam projecting and receiving units with each other. To align the respective optical axes of the beam projecting and receiving units with each other at the time of installation or servicing of the anti-thief security sensor assembly, a servicing worker has to look through a viewing hole of the sighting instrument mounted on the beam projecting and receiving units respectively to adjust the angle of orientation of the beam receiving unit in both vertical and horizontal directions to coarsely align the respective optical axes of the beam projecting and receiving units with each other. Once this has been done, while the signal level proportional to the amount of the infrared beam received by the beam receiver is read out with the use of a level meter such as, for example, a voltmeter electrically connected with and built in the detecting circuit of the beam receiving unit, the angle of orientation of the beam receiver in the vertical and horizontal directions are finely adjusted to render the reading of the signal level to attain more than a predetermined level of the infrared that ought to be received, thereby completing the job of aligning the respective optical axes of the beam projecting and receiving units.
Considering that electro-optical component parts of each of the beam projecting and receiving units including the sighting instrument are generally covered and protected by a cover for each of the beam projecting and receiving units to avoid an unauthorized access thereto, the projector and receiver covers have to be removed in order for a servicing worker to perform adjustment of the sighting instrument and reading of a display on the level meter in each of the beam projecting and receiving units when the optical axis adjustment, i.e., alignment of the respective optical axes of the beam projector and the beam receiver with each other is desired to be carried out.
However, each of the projector and receiver covers is made of a colored material capable of absorbing a certain quantity of the infrared beam passing through the respective cover and, therefore, the infrared beam projected from the beam projector and received by the beam receiver is correspondingly attenuated to a certain extent. For example, in the case of the black-colored cover used for each of the beam projecting and receiving units, about 30% of the infrared beam would be absorbed and attenuated by the respective cover as compared with that before it passes through the respective cover. Accordingly, removal of the projector and receiver covers consequently results in that the amount of the infrared beam received by the beam receiver which has been absorbed and attenuated by the projector and receiver covers increases a quantity substantially equal to the amount of the infrared beam absorbed and attenuated by the projector and receiver covers. In other words, each of the projector and receiver covers is capable of absorbing and attenuating the infrared beam in a quantity corresponding to about 30% thereof and, hence, removal of the projector and receiver covers results substantially in increasing the total infrared beam output of the beam projector being received by the beam receiver.
If the signal level of the infrared beam received by the beam receiver becomes too high as a result of the removal of the projector and receiver covers, not only would an output from an automatic gain control (AGC) circuit employed in the beam receiving unit be saturated, but also the level of the received beam signal, i.e., the level of an output from the beam receiver would attain a value higher than a predetermined level even in the case of misalignment of the respective optical axes of the beam projecting and receiving units with each other because of reflection of the infrared beam from, for example, a wall surface adjacent the site of installation of the anti-thief security sensor assembly. Once this occurs, an accurate optical axis adjustment is indeed difficult to achieve.
In view of the foregoing, the present invention is intended to provide an anti-thief security sensor assembly wherein the optical axis adjustment can be accurately performed even when only one of the projector and receiver covers is physically opened.
In order to accomplish the foregoing object of the present invention, there is provided, in accordance with one aspect of the present invention, an anti-thief security sensor assembly including a beam projecting unit for projecting an infrared beam and a beam receiving unit for receiving the infrared beam projected by the beam projecting unit and operable to detect a human body or the like in the event that the human body or the like traverses the optical path of travel of the infrared beam from the beam projecting unit towards the beam receiving unit. The beam projecting unit includes a mounting base provided with a sensor circuit and a projector cover detachably mounted on the mounting base for enclosing and protecting the sensor circuit. The beam projecting unit also includes an opening detecting switch for detecting a physical opening of the projector cover and a projected beam suppressing circuit operable in response to detection by the opening detecting switch to reduce the amount of the infrared beam emitted from the beam projecting unit to thereby reproduce reduction of the amount of infrared beam caused by the projector cover or reproduce the infrared beam of a quantity or level substantially equal to that having passed through the projector cover.
With this anti-thief security sensor assembly according to the present invention, when the projector cover is physically opened at the time of installation or servicing of the anti-thief security sensor assembly, the opening detecting switch detects such physical opening of the projector cover and provides the projected beam suppressing circuit with a detection signal indicative of the physical opening of the projector cover. The projected beam suppressing circuit, in response to the detection signal from the opening detecting switch, controls the beam projecting unit to cause the latter to emit an infrared beam of a signal level substantially equal to the amount of the infrared beam attenuated by the projector cover as it pass through the latter. In other words, even though the projector cover is physically removed, the beam projecting unit emits the infrared beam at the same level as that when the projector cover is mounted. Accordingly, in the beam receiving unit, by manipulating the sighting instrument so as to render the received beam signal to attain a predetermined signal level, the optical axis of the beam receiving unit can be accurately adjusted relative to that of the beam projecting unit, essentially regardless of whether the projector cover is mounted or removed.
The present invention in accordance with another aspect thereof provides an anti-thief security sensor assembly including a beam projecting unit for projecting an infrared beam and a beam receiving unit for receiving the infrared beam projected by the beam projecting unit and operable to detect a human body or the like in the event that the human body or the like traverses the optical path of travel of the infrared beam from the beam projecting unit towards the beam receiving unit. The beam receiving unit includes a mounting base provided with a sensor circuit and a receiver cover detachably mounted on the mounting base for enclosing and protecting the sensor circuit. The beam receiving unit also includes an opening detecting switch for detecting a physical opening of the receiver cover and a received beam level suppressing circuit operable in response to detection by the opening detecting switch to lower the level of the beam signal received by the beam receiving unit so as to reproduce reduction of the amount of the received infrared beam caused by the receiver cover.
With this anti-thief security sensor assembly according to the present invention, when the receiver cover is physically opened at the time of installation or servicing of the anti-thief security sensor assembly, the opening detecting switch detects such physical opening of the receiver cover and provides the received beam level suppressing circuit with a detection signal indicative of the physical opening of the receiver cover. The received beam level suppressing circuit operates, in response to the detection signal from the opening detecting switch, to reduce a signal level of the infrared beam received by the beam receiving unit, by a quantity corresponding to the amount of the infrared beam absorbed and attenuated by the receiver cover.
Accordingly, even though the receiver cover is removed, a level meter for displaying an output from a detecting circuit in the beam receiving unit provides a display of the received beam signal at the same level as that being received while the receiver cover is mounted. Accordingly, if the use is made of, for example, a communication means in the beam receiving unit for transmitting the received beam level to the beam projecting unit such as disclosed in the Japanese Laid-open Patent Publication No. 4-71099 so that if the accuracy of the optical axis adjustment at the beam projecting unit can be increased, the optical axis adjustment of the beam projecting unit can be advantageously performed regardless of whether the receiver cover is mounted or removed.
The present invention in accordance with a further aspect thereof provides an anti-thief security sensor assembly including a beam projecting unit for projecting an infrared beam and a beam receiving unit for receiving the infrared beam projected by the beam projecting unit and operable to detect a human body or the like in the event that the human body or the like traverses the optical path of travel of the infrared beam from the beam projecting unit towards the beam receiving unit. The beam receiving unit includes a mounting base provided with a sensor circuit and a receiver cover detachably mounted on the mounting base for enclosing and protecting the sensor circuit. The beam receiving unit also includes an opening detecting switch for detecting a physical opening of the receiver cover, and a transmission circuit operable in response to detection by the opening detecting switch to transmit an opening detection signal from the opening detection switch, which is indicative of the physical opening of the receiver cover, from the beam receiving unit to the beam projecting unit. On the other hand, the beam projecting unit is provided with a receiving circuit for receiving the opening detection signal transmitted from the transmission circuit, and a projected beam suppressing circuit operable in response to receipt of the opening detection signal from the opening detection switch via the transmission circuit to reduce the amount of the infrared beam emitted by the beam projecting unit to thereby reproduce the infrared beam of a quantity or level substantially equal to that having passed through the receiver cover.
With this anti-thief security sensor assembly according to the further aspect of the present invention, when the receiver cover is physically opened to perform the optical axis adjustment at the time of installation or servicing of the anti-thief security sensor assembly, the opening detecting switch detects such physical opening of the receiver cover and provides the transmission circuit in the beam receiving unit with an opening detection signal indicative of the physical opening of the receiver cover. The transmission circuit in the beam receiving unit then transmits the opening detection signal from the beam receiving unit to a signal receiving circuit in the beam projecting unit which, in response to receipt of the opening detection signal, activates the projected beam suppressing circuit to control the beam projecting unit so as to cause the latter to emit the infrared beam of a signal level reduced by a quantity corresponding to the amount of the infrared beam absorbed and attenuated by the receiver cover.
Accordingly, in the beam receiving unit, even while the projector cover is remain mounted, by manipulating the sighting instrument in the beam receiving unit so as to render the received beam signal to attain a predetermined signal level, the optical axis of the beam receiving unit can be accurately adjusted relative to that of the beam projecting unit. Also, since the projector cover need not be removed, the workability can be advantageously increased.
In further preferred embodiments of the present invention, the present invention provide the beam projecting and receiving units both employed in the anti-thief security sensor assembly of the structure discussed above.
It is to be noted that the term xe2x80x9cphysical openingxe2x80x9d used in connection with the projector and receiver cover in the description made hereinabove and hereinafter is intended not only to means that the cover is hingedly opened relative to the associated base to which it is hinged, but also to means that the cover is removed away from the associated base and is thus used in the sense that when the cover is opened, internal component parts covered and projected by such cover are rendered open to the outside regardless of whether the cover remains hingedly affixed to the associated base or whether it be separated from the associated base.